Conventionally, in an injection molding machine, molds (a fixed mold and a movable mold) are fixed to a fixed platen and a movable platen, respectively, and the movable platen is driven to move so as to come closer to or separate from the fixed platen, and mold shutting and mold opening of the molds are accomplished. While the molds are shut, a molten synthetic resin is injected into cavities inside the molds and an article to be injection-molded is molded, and then, the molds are opened and the injection-molded article is ejected by an ejector mechanism.
Here, fixation of the molds to the fixed platen and the movable platen in the injection molding machine is often performed using multiple bolts or hydraulic clamping devices. However, in recent years, a mold fixation device where a magnet platen (adhesion plate) is attached to the fixed platen and the movable platen, respectively, and the molds are adhered and fixed to the fixation surfaces of the magnet platens by a magnetic force generated by the magnet platen is about to be practically used.
In the injection molding machine of Patent Literature 1, a large-sized magnet platen made of a permanent magnet is provided to the fixed platen and the movable platen of the injection molding machine, respectively.
In the injection molding machine of Patent Literature 2, a mold adhesion platen is attached to the movable platen and an assembly ring is fixed to a center portion of this mold adhesion platen, and many lateral cylindrical alnico magnets are arranged in the mold adhesion platen, and a large coil is wound around the circumference of the alnico magnets, respectively, and a large-sized circular plate is arranged in front of the alnico magnets and externally fitted into the assembly ring.
In the injection molding machine of Patent Literature 3, the configuration is such that a clamp plate where multiple magnet units are incorporated is fixed to the fixed platen and the movable platen, respectively, and the molds are fixed to the fixation surfaces of the clamp plates by the magnetic force generated by the multiple magnet units, respectively.
Each magnet unit has a steel block, multiple permanent magnets arranged around the circumference of this steel block, an alnico magnet arranged at the rear surface side of the steel block and a coil wound around the circumference of this alnico magnet, and the direction of a magnetic field of the alnico magnet can be switched to the opposite direction according to the direction of power distribution supplied to the coil. In the clamped state to adhere the molds, a magnetic field where the mold become a portion of a magnetic path is generated, and in the unclamped state to release the fixation of the molds, another magnetic field where a magnetic circuit not using the mold as a portion of the magnetic path is generated by switching the direction of the magnetic field of the alnico magnet.
In other words, in order to convey the mold to the injection molding machine, a method where multiple in-platen rollers are provided in the lower portions of the fixed platen and the movable platen, respectively, and when conveying the molds, both flanges of these molds are accepted by the in-platen rollers at the both sides, and these are moved on the in-platen rollers is adopted.
However, with the injection molding machine without the in-platen rollers, another method where a mold is hung with a crane and the mold is conveyed in between the fixed platen and the movable platen from the upper side of the injection molding machine is also adopted.                Patent Literature 1: Japanese Utility Model Application H5-24330        Patent Literature 2: Japanese Patent Application Laid-Open No. 2001-88133        Patent Literature 3: Japanese Patent Application Laid-Open No. 2005-169840        